(a) Field of the Invention
This invention relates to a mechanical sealing device, and more particularly to a cooling mechanism for use with a mechanical sealing device for a rotary shaft rotating at a high speed.
(B) Description of the Prior Art
In prior art mechanical sealing devices, a rotary shaft extends through stationary casings, and an attaching ring and a seal ring are arranged in surrounding but concentric relation to the rotary shaft with a resilient bellows interposed therebetween. The attaching ring is affixed to one of the casings, while the seal ring is urged against a mating ring fitted on the rotary shaft by means of a resilient bellows in sliding relation thereto. Sliding contact of the seal ring with the mating ring produces heat due to friction and thereby raises the temperature of the rings.
In an effort to solve this heating problem, oil is sprayed over the surface of the mating ring for cooling same. However, such spraying does not completely cool the mating ring.
For better understanding of the sealing device according to the present invention, a prior art mechanical sealing device will be described in more detail with reference to FIG. 1.
A prior art mechanical sealing device in general consists of: a mating ring 1 which is fitted on a rotary shaft 8 and rotated together therewith; a seal ring 2 having a surface adapted to abut the surface of the mating ring 1 on its one side; a supporting ring 3 for supporting the seal ring 2 on its back surface; a mechanical-seal-outer cylinder 4 fitted in a casing 6; and a resilient bellows 5 whose sides are sealingly coupled to the supporting ring 3 and mechanical-seal-outer cylinder 4. The outer cylinder 4 is fitted in an annular groove defined in the wall of a bore in the stationary casing 6 with an O-ring 17 interposed between the outer cylinder 4 and the casing 6 for maintaining a seal therefor. The casing 6 is fastened to another casing 7 by means of bolts and nuts not shown. The rotary shaft 8 extends through the casings 6, 7 and is supported by known bearing means (not shown) which are rigidly fitted in the casings 6, 7. The mating ring 1 is fitted on the shaft 8 on its boss position, and is urged against an annular shoulder portion of the shaft 8 in the axial direction by means of a spacer 9 to thereby rotate tpgether with the spacer 9 and the shaft 8. As has been described earlier, the seal ring 2 is supported by the supporting ring 3 which in turn is coupled to one edge of the resilient bellows 5, the other edge thereof being coupled to a flange 4a of the outer cylinder 4 affixed to the casing 6. Thus, the seal ring 2 remains stationary. Accordingly, spaces 10 and 11 defined on the axially opposite sides of the mechanical seal device are sealed from each other by means of the mating ring 1, seal ring 2, bellows 5, and outer cylinder 4, the bellows 5 urging the seal ring 2 against the surface of the mating ring 1.
Relative sliding contact of the seal ring 2 with the mating ring 1 produces heat due to friction. In an effort to solve this heating problem, oil is sprayed in the form of jet 15 through a nozzle 14, communicated with an oil passage 13 provided in the casing 7, over the back surface of the mating ring 1 to thereby cool it. After cooling, oil is discharged outside through a drain 16 provided in the casing 7.
For enhancing the sealing effect of the mechanical sealing device of the type shown in FIG. 1, the force to urge the seal ring 2 against the mating ring 1 should be increased. However, an increase in that force leads to an increase in the amount of heat produced due to friction. The seal ring 2 in general is however made of a heat resistant and abrasion-resistant material, such as carbon. On the other hand, the mating ring 1 is made of a metal, taking into consideration the combined use with the type of material forming the seal ring and its strength upon high speed rotation. In addition, the sliding surface of the mating ring 1 is subjected to a surface-hardening treatment such as carburizing and nitriding. Accordingly, if the force to urge the seal ring 2 against the mating ring 1 is extremely high, or if the rpm of the mating ring is increased, then the amount of heat produced due to friction is increased. This increase in turn leads to an increase in temperature of the mating ring, lowering in hardness, or seizure of the sliding surface of the mating ring 1, resulting in shortened service life or premature failure. To overcome these shortcomings, oil is sprayed over the surface of the mating ring 1 to cool same. However, when the rpm of the rotary shaft is increased, to say as high as several hundred thousand rpm, then oil sprayed on the mating ring 1 fails to cling to the surface of the mating ring 1, because of the extremely high peripheral speed of the mating ring 1, i.e., the extremely large centrifugal force acting on the oil jets. For this reason, oil fails to flow along the surface of the mating ring 1 in contact therewith, thus lowering the cooling effect.
For improving the cooling effect of the mechanical sealing device having the aforesaid arrangement, the amount of oil being supplied can be increased by raising the pressure of the oil. However, if the amount of the oil being supplied is increased excessively, then the oil fills around the mating ring, because the oil cannot flow through the drain at a rate equal to or faster than the oil being supplied. This draining problem leads to another problem of increased friction between the surfaces of the mating ring and the oil in contact therewith when the mating ring rotates at high rpm.